1. Field of the Invention
This invention relates to circuit breakers such as wiring breakers and earth leakage breakers, and more particularly to the mounting of accessories such as an alarm switching, auxiliary switch, undervoltage trip unit, and voltage trip unit which are built in such a circuit breaker.
2. Description of the Prior Art
Of those accessories, the auxiliary switch is to electrically indicate the "on" and "off" states of the circuit breaker, and the alarm switch is to electrically indicate the trip of the circuit breaker, the undervoltage trip unit is to trip the circuit breaker when the circuit voltage is decreased to lower than a predetermined value, and the voltage trip unit is to electrically trip the circuit breaker at a remote position.
A wiring breaker or earth leakage breaker comprises: an container of electrically insulated material which is made up of a casing and a cover; and a switching mechanism set in the insulated container. The aforementioned accessories are built in the insulated container according to the specification during manufacture of the circuit breaker. Therefore, it is impossible for the user to exchange the accessories for other ones or to add desired accessories to the circuit breaker.
In order to overcome this difficulty, the following circuit breaker has been proposed in the art (cf. Japanese Patent Application (OPI) No's 124270/1979, 52360/1989, and 144819/1990 (the term "OPI" as used herein means an "unexamined published application")). In the circuit breaker, the accessories are not built in the insulated container, and instead they are formed as units, and detachably mounted in recesses from outside which are formed in the cover, so that the user can replace them or add desired accessories.
In a conventional circuit breaker of this type, the accessories are mounted directly on the cover. Hence, the circuit breaker suffers from the following difficulties: Accessories which can be mounted on the cover are limited by the configurations of the recesses formed in the cover, and accordingly the combination of accessories, and the selection of specifications are unavoidably small in the degree of freedom.
For instance, micro-switches used for the auxiliary switch and the alarm switch are different in configuration and in size depending on the manufacturers, contact structures and rating. Therefore, even if they are formed as units, it is difficult to unify them in configuration and size. Accordingly, it is necessary to provide a variety of covers different in recess configuration; however, it is not economical to do so. Furthermore, it is limited to make the recesses intricate in configuration because a great internal pressure acts on the cover when the circuit breaker is operated to interrupt short-circuit current. Thus, the conventional circuit breaker cannot meet the requests of the user.